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use clippy_utils::diagnostics::span_lint_and_sugg;
use clippy_utils::is_from_proc_macro;
use rustc_errors::Applicability;
use rustc_hir::def::{DefKind, Res};
use rustc_hir::{Pat, PatKind, QPath};
use rustc_lint::{LateContext, LateLintPass};
use rustc_session::declare_lint_pass;
declare_clippy_lint! {
/// ### What it does
/// Checks for struct patterns that match against unit variant.
///
/// ### Why is this bad?
/// Struct pattern `{ }` or `{ .. }` is not needed for unit variant.
///
/// ### Example
/// ```no_run
/// match Some(42) {
/// Some(v) => v,
/// None { .. } => 0,
/// };
/// // Or
/// match Some(42) {
/// Some(v) => v,
/// None { } => 0,
/// };
/// ```
/// Use instead:
/// ```no_run
/// match Some(42) {
/// Some(v) => v,
/// None => 0,
/// };
/// ```
#[clippy::version = "1.86.0"]
pub UNNEEDED_STRUCT_PATTERN,
style,
"using struct pattern to match against unit variant"
}
declare_lint_pass!(UnneededStructPattern => [UNNEEDED_STRUCT_PATTERN]);
impl LateLintPass<'_> for UnneededStructPattern {
fn check_pat(&mut self, cx: &LateContext<'_>, pat: &Pat<'_>) {
if !pat.span.from_expansion()
&& let PatKind::Struct(path, [], _) = &pat.kind
&& let QPath::Resolved(_, path) = path
&& let Res::Def(DefKind::Variant, did) = path.res
{
let enum_did = cx.tcx.parent(did);
let variant = cx.tcx.adt_def(enum_did).variant_with_id(did);
let has_only_fields_brackets = variant.ctor.is_some() && variant.fields.is_empty();
let non_exhaustive_activated = !variant.def_id.is_local() && variant.is_field_list_non_exhaustive();
if !has_only_fields_brackets || non_exhaustive_activated {
return;
}
if is_from_proc_macro(cx, *path) {
return;
}
if let Some(brackets_span) = pat.span.trim_start(path.span) {
span_lint_and_sugg(
cx,
UNNEEDED_STRUCT_PATTERN,
brackets_span,
"struct pattern is not needed for a unit variant",
"remove the struct pattern",
String::new(),
Applicability::MachineApplicable,
);
}
}
}
}
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